Data mirroring between controllers in an active-active controller pair

Abstract

A data storage system that includes first and second controllers is provided. Data is mirrored from one controller to the other controller according to different steps depending on the amount of data to be mirrored. When the data to be mirrored is less than or equal to a predetermined number of bytes, one less interrupt is generated than when the data to be mirrored is greater than the predetermined number of bits.

Description

FIELD OF THE INVENTION[0001]The present invention relates to performance enhancements for redundant array of inexpensive disks (RAID) storage systems and more particularly to a method and system for enhancing performance of mirroring operations between controllers in an active-active controller pair.BACKGROUND OF THE INVENTION[0002]A typical data processing system generally includes one or more storage units or devices which are connected to a host computer either directly or through a control unit and a channel. The function of the storage units is to store user data and other information (e.g., program code) which the host computer uses in performing particular data processing tasks.[0003]Various types of storage units are used in current data processing systems. A typical system may include one or more large capacity tape units and / or disk drives connected to the system through respective control units for storing data. However, a problem exists if one of the storage units fails ...

AI Technical Summary

Benefits of technology

[0023]Based on the foregoing, several benefits of the present invention are readily seen. The system causes fewer interrupts to the second controller when the data is less than or equal to the predetermined number of bytes, which may result in enhanced performance of the second controller. The system and method may also consume less channel bandwidth when conducting mirroring operations.

Problems solved by technology

However, a problem exists if one of the storage units fails such that information contained in that unit is no longer available to the system.

Generally, such a failure will shut down the entire computer system, which can create a problem for systems which require data storage systems to have high availability.

In these type of applications, unavailability of data stored on the RAID system can result in significant loss of revenue and / or customer satisfaction.

If the controller that received the user data subsequently suffers a failure prior to writing the user data to the disk array 30, the data can be lost.

However, if the controller mirrors the user data prior to sending the host 14 a reply that the data has been written, a failure of the controller can still be recovered without loss of the data, using the copy of the user data that was mirrored to the other controller.

In such a situation, the sending controller will, after a predetermined time, resume sending the data, causing an additional interrupt.

Servicing these interrupts can take a significant portion of the processing resources of a controller.

As can be seen, for small writes, mirroring a 1 Kbyte metadata message can be inefficient.

When a RAID system is receiving many read and write requests from the host 14, the disk channel 34 can become bandwidth limited, increasing the time required to complete a read or write operation.

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